KR19990078225A - Surface light source device of side light type and liquid crystal display - Google Patents

Abstract

The LCD panel LP of the liquid crystal display device 2 is illuminated with a side light type surface light source device 1 for backlighting. The surface light source device 1 includes a plurality of sets of primary light source primary light guide plates. When the fluorescent lamp 11A is turned on, the illumination light LA is introduced into the light guide plate 7A, emitted from the exit surface 7AO, and transmitted to the light guide plate 7B. Projections are formed on the rear surface 7AR, and the illumination light is prevented from being diffused in the left and right directions when viewed from the incident end surface 7AI. The light transmitted to the light guide plate 7B is emitted obliquely forward from the exit surface 7BO (LA1). The prism sheet 9 converts this into output illumination light LA2 in the front direction, and illuminates the LCD panel LP through the light diffusion sheet 10. When the fluorescent lamp 11B is turned on, the illumination light LB is introduced into the light guide plate 7B and is emitted from the emission surface 7BO. Light transmitted to the light guide plate 7B is emitted obliquely forward from the emission surface 7BO (LB1). The prism sheet 9 converts this into the output illumination light LB2 in the front direction, and illuminates the LCD panel LP through the light diffusion sheet 10. The drive currents (including selective control of lighting / lighting off) of the fluorescent lamps 11A and 11B are controlled in the drive circuit 4. Various directing characteristics can be realized according to the inclination angle of the prism inclined surface of the prism sheet arranged along the exit surface 7BO. For example, selective emission in the other two directions and simultaneous emission in the other two directions can be realized.

Description

Side light type surface light source device and liquid crystal display device {SURFACE LIGHT SOURCE DEVICE OF SIDE LIGHT TYPE AND LIQUID CRYSTAL DISPLAY}

The present invention relates to a side light type surface light source device and a liquid crystal display device to which the device is applied for backlighting. In more detail, the surface light source device and the device of the type employing a plurality of sets of a primary light source and a light guide plate are described. The present invention relates to a liquid crystal display device in which is applied to backlighting.

The side light type surface light source device is a well-known fact as a device for outputting an illumination light beam having an optical end area, and is applied to backlighting of a liquid crystal display device, for example. The side light type surface light source device arranged for backlighting supplies illumination light from the back of the liquid crystal panel.

In general, a side light type surface light source device includes a light guide plate and a primary light source. One of the major surfaces of the light guide plate provides an exit surface, and the other provides a rear surface. The primary light source is disposed on the incident end side of the light guide plate, and supplies the primary light to the light guide plate through the incident end surface. This arrangement is suitable for thinning the overall shape.

In the primary light source, a rod-shaped light source such as a cold cathode tube is usually used. In some cases, a point light source such as an LED (light emitting diode) is employed. Illumination light emitted from the primary light source is introduced into the light guide plate through an incident cross section of the light guide plate. The introduced illumination light propagates in the light guide plate, and in the process, the illumination light is output from the exit surface of the light guide plate. As typical light guide plates, flat light guide plates and wedge cross-sectional light guide plates having the same thickness are known. In the case of employing electrons, primary light is supplied to the light guide plate through one or more end faces (minor surfaces). When the latter is adopted, primary light is supplied to the light guide plate through the thick section. These cross sections through the primary light are called incident cross sections.

Typical primary light sources for primary light supply are, for example, rod-shaped light sources such as cold cathode tubes (fluorescent lamps). It is also known to employ a point light source such as an LED as the primary light source.

One major surface of the light guide plate provides an exit surface from which the illumination light is emitted. It is generally known that the main exit direction (priority exit direction) is inclined forward (primary light supply direction) with respect to the plane perpendicular to the incident cross section. In order to correct this and obtain the light output in the front direction, a light control member such as a prism sheet may be employed along the exit surface.

Side light type surface light source devices that provide powerful illumination light output are desired for backlighting liquid crystal display devices applied to, for example, car navigation systems. It is also desired that the intensity of the illumination light output be adjustable over a wide range. This is because the optimum brightness of the display changes according to the environment such as day and night, blue and rainy weather. For example, in daytime driving in Chuncheon, in order to endure strong external light, very strong illumination light output backlighting is required. On the other hand, the backlighting of the strong illumination light output at night is not appropriate because it gives too intense indication, and a weak illumination light output is preferable.

There is a need for a side light type surface light source device that provides an illumination light output having bidirectional directivity depending on the application. For example, in a liquid crystal display device applied to a car navigation system, it is required to provide bright display to one or both of the driver and the assistant of the side seat, depending on the situation.

Directivity is desired to be switchable according to the use situation. For example, when observing the LCD by the driver alone or the assistant alone, it is sufficient that one of the two priority outputs is valid. When both the driver and the assistant observe the LCD, it is preferable that both of the two priority outputs are effective.

It is difficult to find a side light type surface light source device and a liquid crystal display device in the prior art that satisfy such various demands and demands and have a simple structure. Background Art A light source device for supplying light at both incident cross sections of a light guide plate is known, but does not satisfactorily satisfy the above various demands and demands.

A general object of the present invention is to provide a side light type surface light source device and a liquid crystal display device capable of satisfactorily satisfying the above various demands and demands.

That is, one object of the present invention is to provide a side light type surface light source device which can adjust the intensity of illumination light output over a wide range. Further, another object of the present invention is to apply this to a liquid crystal display device so that good display can be easily obtained without being influenced by the environment.

It is still another object of the present invention to provide a side light type surface light source device that provides an illumination light output having bidirectional directivity. Further, another object of the present invention is to apply this to a liquid crystal display device so as to obtain a display suitable for observation in two different directions, in particular in one of those two directions.

1 is an exploded perspective view showing a liquid crystal display device according to a first embodiment.

FIG. 2 is a cross-sectional view of the arrangement shown in FIG. 1. FIG.

FIG. 3 is a graph showing directing characteristics of illumination light under conditions in which the prism sheet is removed and the first primary light source is independently lit in the first and fourth embodiments. FIG.

FIG. 4 is a graph showing directing characteristics of illumination light in a case where the prism sheet is removed and the second primary light source is independently lit in the first and fourth embodiments. FIG.

FIG. 5 is a graph showing directing characteristics of illumination light in a case where the prism sheet is removed and the first and second primary light sources are simultaneously lit in the first and fourth embodiments. FIG.

Fig. 6 is a sectional view for explaining the action of the prism sheet employed in the first embodiment.

FIG. 7 is a graph showing directing characteristics of illumination light in a condition of turning on a first primary light source alone in the first embodiment; FIG.

FIG. 8 is a graph showing directing characteristics of illumination light under conditions in which the second primary light source alone lights up in the first embodiment; FIG.

FIG. 9 is a graph showing directing characteristics of illumination light under conditions in which the first and second primary light sources are simultaneously lit in the first embodiment. FIG.

10 is a cross-sectional view illustrating an arrangement in which one light guide plate receives light from a plurality of light source elements.

11 is an exploded perspective view for explaining an arrangement employing three or more light guide plates.

12 is an exploded perspective view showing a liquid crystal display device according to a second embodiment.

FIG. 13 is a sectional view of the arrangement shown in FIG. 12; FIG.

Fig. 14 is a sectional view for explaining the action of the prism sheet employed in the second embodiment.

FIG. 15 is a graph showing directing characteristics of illumination light under conditions in which the first primary light source is independently lit in the second embodiment; FIG.

FIG. 16 is a graph showing directing characteristics of illumination light under conditions in which the second primary light source alone lights up in the second embodiment; FIG.

FIG. 17 is a graph showing directing characteristics of illumination light under conditions in which the first and second primary light sources are simultaneously lit in the second embodiment; FIG.

18 is an exploded perspective view illustrating another arrangement in which three or more light guide plates are used.

* Description of the symbols for the main parts of the drawings *

2: LCD

3A: primary light source

3B: second primary light source

4: driving circuit

7A: first light guide plate

7B: second light guide plate

8: half sheet

9: prism sheet

10: light diffusion plate

11A, 11B: Fluorescent Lamp

12A, 12B: Reflector

The side light type surface light source device according to the present invention includes a first light guide plate, a first primary light source arranged in parallel with the first light guide plate, a second light guide plate, a second primary light source arranged in parallel with the second light guide plate, and a first primary light source. And a driving circuit for driving the light source and the second primary light source.

In addition, two major surfaces of the first LGP provide a first exit surface and a first back surface, while one minor surface of the first LGP provides a first incident surface, and two of the second LGPs A major surface of the second light guide plate and a second back surface, one minor surface of the second light guide plate provides a second incidence cross-section, the first light guide plate and the second light guide plate, the second back surface is the first output Laminated to be arranged along the plane continuously.

The first incidence cross section and the second incidence cross section are located on opposite sides with respect to the stacked arrangement, and a light control member for controlling the directivity of the illumination output light is arranged along the second emission surface. Preferably, the driving circuit can extinguish only one of the first primary light source and the second primary light source.

Moreover, it is preferable to employ | adopt what has a wedge-shaped cross section as a 1st light guide plate and a 2nd light guide plate, respectively, and set a 1st incident cross section and a 2nd incident cross section in the wedge-shaped thick side.

It is preferable that a plurality of rows of projections are formed on the first back surface, and each of the projections includes a pair of inclined surfaces that are disposed substantially perpendicular to the first incidence end surface.

When bidirectional directivity is not desired, the directivity toward the front direction of the second emission surface is to both the illumination output light output by the first primary light source and the illumination output light output by the second primary light source as the light control member. It is employed to correct.

In this case, a plurality of rows of projections are formed on the inner surface of the light control member which is typically used, and each of the projections includes a pair of inclined surfaces that are continuously arranged substantially parallel to the second incidence end surface.

In a typical embodiment, the first and second primary light sources are rod-shaped light sources arranged such that the extending directions are substantially parallel.

The above and other features of the present invention will be readily understood in the detailed description of the embodiments made with reference to the accompanying drawings.

(1) First embodiment

1 and 2, a side light type surface light source device 1 is arranged for backlighting of an LCD panel (liquid crystal display panel), and constitutes a liquid crystal display device 2 (FIG. 2). The liquid crystal display device 2 is applied to a display in a car navigation system, for example. The surface light source device 1 includes first and second light guide plates 7A and 7B, and correspondingly includes first and second primary light sources 3A and 3B and a driving circuit 4 for driving them. .

The light guide plates 7A and 7B consist of scattering light guides. A scattering light guide is a material having a scattering ability therein, and is composed of, for example, a matrix made of polymethyl methacrylate (PMMA) and "birefringent fine particles" uniformly dispersed in the matrix. Particles having a refractive index different from that of the matrix in light transmission are employed as "birefringent fine particles".

The two major surfaces of the first light guide plate 7A provide an exit surface 7AO (first exit surface) and a rear surface 7AR (first rear surface). Two major faces of the second light guide plate 7B provide an exit face 7BO (second exit face) and a back 7BR (second back face).

The first and second light guide plates 7A and 7B are laminated so that the second back surface is continuously disposed along the first emission surface. In this embodiment, the 1st and 2nd light guide plates 7A and 7B have the same wedge-shaped cross section, and are arrange | positioned so that the 1st emitting surface 7AO may follow the 2nd rear surface 7BR. The first exit surface 7AO and the second rear surface 7BR provide inclined surfaces having substantially the same area, and the inclined surfaces face each other with a thin air layer therebetween. This arrangement provides a compact overall structure with the same thickness.

One minor surface of the first light guide plate 7A provides the first incident end surface 7AI. In addition, as shown by the circle B in FIG. 1, one minor surface of the second light guide plate 7B provides the second incident end surface 7BI. The first incident cross section 7AI and the second incident cross section 7BI are located opposite to each other with respect to the light guide plates.

The primary light sources 3A and 3B include, for example, rod-shaped fluorescent lamps (cold cathode tubes) 11A and 11B, respectively, and light emitting sources and reflecting plates 12A and 12B. The reflecting plates 12A and 12B are behind the primary light sources 3A and 3B and open toward the incident end surfaces 7AI and 7BI. The reflecting plates 12A and 12B are made of a sheet material of specular reflection or diffuse reflection, for example.

The drive circuit 4 incorporates an inverter and supplies electric power to one or both of the fluorescent lamps 11A and 11B. The power supply can be adjusted continuously or stepwise. Furthermore, not only simultaneous lighting and simultaneous lighting of both lamps but also one of the lights can be turned on and the other can be turned off.

The fluorescent lamp 11A is disposed along the incident end surface 7AI, and the fluorescent lamp 11B is disposed along the incident end surface 7BI. One or both of the fluorescent lamps 11A and 11B supplies primary light to one or both of the first and second light guide plates 7A and 7B according to the operation mode of the drive circuit 4.

As shown by circle (A) in FIG. 1, many protrusion lines are formed in the 1st back surface. Each of the projection lines includes pairs of inclined surfaces 7AE and 7AF which are disposed substantially perpendicular to the first incident cross section 7AI. These inclined surfaces 7AE and 7AF are closer to the front direction with respect to the in-plane parallel to the incidence end surface 7AI in terms of the directivity (priority exit direction) of the light output at the exit surface 7AO (also at exit surface 7BO). To act. In addition, compared with the case where the rear surface 7AR is assumed to be a flat surface (no inclined surfaces 7AE and 7AF), it emits from the output surface 7AO with less internal reflecting number, so that the emission efficiency is improved.

The reflective sheet 8 is disposed along the first back surface 7AR. The reflective sheet 8 is made of, for example, a metal foil of specular reflection or a white PET film of diffuse reflection. The reflective sheet 8 reflects the light leaked from the back surface 7AR and returns to the light guide plate 7A, thereby preventing the loss of the light energy.

The prism sheet 9 as the light control member is made of a transparent sheet material such as polycarbonate. The prism sheet 9 is disposed along the second emission surface 7BO in an orientation in which the prism surface faces the emission surface 7BO. A large number of protrusions are formed on the prism face.

As shown by circle C in FIG. 1, each of the protrusions includes pairs of inclined surfaces 9A and 9B which are continuously arranged substantially parallel to the incident end surface 7BI. The inclined surface pairs 9A and 9B are directly connected to each other and give a triangular cross section to each of the protrusion rows. The prism sheet 9 corrects the directivity in the plane perpendicular to the incidence section 7BI (and 7AI). Details of the corrective action will be described later. The output light of the prism sheet 9 illuminates the LCD panel LP via the light diffusion plate 10.

The light diffusion plate 10 has weak light scattering power, alleviates the sharpness of the directivity of the illumination light, and increases the softness. In addition, the number of protrusions and the edges of the light guide plate 7B formed on the prism sheet 9 and the back surface 7AR are made inconspicuous.

It is preferable that a light scattering pattern for promoting the emission from the light guide plate 7A or 7B is formed on one or both of the emission surfaces 7AO and 7BO. This light scattering pattern uniforms the emission intensity at the exit surfaces 7AO and 7BO.

The scattering pattern is formed so that it is difficult to visually check from the emission surface 7AO or 7BO side. For example, a large number of micro roughness areas of a dot shape of 80 μm or less may form a scattering pattern. It is preferable that the distribution of the rough surface area be in an irregular arrangement. This is because the irregular arrangement prevents the generation of moire fringes due to the mutual relationship with the regular structure (for example, the electrode arrangement) of the LCD panel LP. When the fluorescent lamp 11A is turned on, the illumination light LA is introduced into the light guide plate 7A and propagates toward the thin end. During this time, repeated reflection by the emission surface 7AO and the back surface 7AR, scattering by the internal scattering ability, and scattering by the light scattering pattern on the emission surface 7AO occur. The component which cleared the critical angle condition at the time of internal incidence to the exit surface 7AO exits from the exit surface 7AO and enters the light guide plate 7B. In order to increase the light transmission efficiency from the first light guide plate 7A to the second light guide plate 7B, the rear surface 7BR is preferably a mirror surface.

In addition, as described above, the plurality of inclined surface pairs 7AE and 7AF formed on the rear surface 7AR enters the directivity (priority emission direction) of the light output at the emission surface 7AO by the action of internal reflection or the like. It is made closer to the front direction with respect to the in-plane parallel to the cross section 7AI. The modified directivity in this manner is almost maintained even through the light guide plate 7B. Therefore, the directivity of the illumination output at the exit surface 7BO is closer to the front direction with respect to the surface parallel to the incident end surface 7AI or 7BI.

It should be noted here that the light emitted from the exit surface 7AO is inclined greatly toward the front (incident cross section 7BI side) in the plane perpendicular to the incident cross section 7AI. This directivity is almost maintained even through the light guide plate 7B. Therefore, the directivity of the illumination output at the exit surface 7BO is greatly inclined toward the front (incident cross section 7BI side) in the plane perpendicular to the incident cross section 7AI or 7BI.

On the other hand, when the fluorescent lamp 11B is turned on, the illumination light LB is introduced into the light guide plate 7B and propagates toward the thin end. During this time, repeated reflection by the emission surface 7BO and the back surface 7BR and scattering by the internal scattering ability occur. The component which cleared the critical angle condition at the time of internal ingress to the exit surface 7BO exits from the exit surface 7BO. Very little but some light is introduced from the back surface 7BR to the light guide plate 7A. Most of such light is re-emitted from the exit surface 7AO via various optical paths, and returns to the light guide plate 7B.

It should be noted that the illumination light supplied from the fluorescent lamp 11B and exiting from the exit surface 7BO is inclined toward the front (incident cross section 7AI side) in the plane perpendicular to the incident cross section 7BI. .

That is, at the time of exit from the exit surface 7BO, the light output by the fluorescent lamp 11A and the light output by the fluorescent lamp 11B are in-plane perpendicular to the incident end surface 7AI or 7BI. They are inclined to the opposite sides with respect to the normal line (frontal direction) on the exit surface 7BO.

For convenience of explanation, the former is represented by the light beam LA1 and the latter by the light beam LB1. In this example, the inclination angle with respect to the exit surface 7BO of LA1, LB1 is about 23 degrees. Light rays LA1 and LB1 become light rays LA2 and LB2 after passing through the prism sheet 9. That is, the surface light source device 1 outputs the light beam LA2 when only the fluorescent lamp 11A is lit, and outputs the light beam LB2 when only the fluorescent lamp 11B is lit. When the fluorescent lamps 11A and 11B are turned on at the same time, the light beams LA2 and LB2 are output.

In order to verify the directivity of the emitted light represented by LA1 and LB1, the following measurements were performed. First, in the first embodiment, the prism sheet 9 is removed and the directivity characteristic of the outgoing light on the exit surface 7BO is measured under conditions that the fluorescent lamp 11A (first primary light source) lights up alone. The results are shown in the graph of FIG.

Similarly, when the prism sheet 9 is removed and the fluorescent lamp 11B (second primary light source) is lit alone, the result shown in the graph of FIG. 4 is obtained. In addition, when the prism sheet 9 is removed and both lights 11A and 11B are simultaneously lit, the result shown in the graph of FIG. 5 is obtained.

In these graphs and various graphs (FIGS. 7 to 9 and 15 to 17) described later, the long side direction of the light guide plate 7A is the Y direction, based on the normal direction of the exit surface 7BO of the light guide plate 7B. The direction along the incident surface 7AI is defined as the X direction.

Xθ is an angle indicating the direction with respect to the plane along the incident surface 7AI, and Yθ is an angle indicating the direction with respect to the plane perpendicular to the incident surface 7AI. The sign of Xθ is positive in the left and right and negative in the right side when viewed from the incident surface 7AI. The sign of Yθ is positive in the front side and negative in the near side as seen from the incidence surface 7AI. The normal direction of the exit surface 7BO corresponds to Xθ = Yθ = 0. Light intensity is plotted as height in the Xθ-Yθ plane.

In the measurement results of FIGS. 3 and 4, it is understood that the illumination light represented by LA1 has a directivity inclined to the right in FIG. 2, and the illumination light represented by LB1 has a directivity inclined to the left in FIG. 2. This point is also understood in the curve of the two ridges drawn in the graph of FIG. Naturally, the graph of FIG. 5 corresponds to the addition of the graph of FIG. 3 and the graph of FIG.

It should be noted here that the two ridge curves shown in FIG. 5 are shown at angular positions that are nearly symmetrical with respect to the frontal direction (Xθ = 0). One ridge corresponds to LA1 and the other ridge corresponds to LB1.

Therefore, if both LA1 and LB1 can be bent in the front direction (Xθ = 0), either the single lamp of the fluorescent lamp 11A, the single lamp of the fluorescent lamp 11B, or the simultaneous lighting of the fluorescent lamps 11A and 11B are possible. Also in the illumination light LA2, LB2 and LA2 + LB2 which preferentially exit in the frontal direction.

As the prism sheet 9, one having such a bending action is employed.

In this embodiment, in order to correspond to the result of FIGS. 3-5, the right angle (alpha) which the inclined surfaces 9A and 9B make is set to (alpha) = 66 degree. The inclination angles (angle formed with respect to the general surface of the prism sheet 9) of the inclined surfaces 9A and 9B are equal to each other (inclined angle = 57 degrees).

As shown in FIG. 6, the illumination light LA1 is introduced into the prism sheet 9 from the inclined surface 9B, and is then reflected by the inclined surface 9A to output the illumination light LA2 almost in the front direction. Similarly, the illumination light LB1 is introduced into the prism sheet 9 from the inclined surface 9A, and is then reflected by the inclined surface 9B to output the illumination light LB2 almost in the front direction.

The value of the optimum right angle α varies slightly depending on the directivity characteristic of the illumination light LA1 and LB1 (angular position of the ridge line in FIG. 5), the refractive index of the prism sheet 9, and the like. In general, the right angle α is determined by design based on the above measurement or calculation (Snell's law).

The action of the prism sheet 9 in this example is easily understood in the graphs of FIGS. 7 to 9. FIG. 7 is a graph showing directing characteristics of illumination light under conditions of illuminating the fluorescent lamp 11A (first primary light source) alone in the first embodiment. That is, the prism sheet 9 is added to the arrangement | positioning which obtained the result of FIG. 3, and the directivity characteristic of the output light of the prism sheet 9 is measured.

Similarly, FIG. 8 is a graph showing the directing characteristic of illumination light under the condition of lighting the fluorescent lamp 11B (second primary light source) alone in the first embodiment. That is, the prism sheet 9 is added to the arrangement | positioning which obtained the result of FIG. 4, and the directivity characteristic of the output light of the prism sheet 9 is measured.

FIG. 9 is a graph showing directing characteristics of illumination light under conditions of simultaneously lighting the fluorescent lamps 11A and 11B (first and second primary light sources) in the first embodiment. That is, the prism sheet 9 is added to the arrangement | positioning which obtained the result of FIG. 5, and the directivity characteristic of the output light of the prism sheet 9 is measured.

Also in any of the graphs of FIGS. 7 to 9, a plot having a peak almost in the normal direction must be obtained. In addition, in FIGS. 7-9, the plot of light intensity is displayed in the X (theta) -Y (theta) plane lower than FIG. 3-5.

Illumination lights LA2 and LB2 illuminate the LCD panel LP through the light diffusion sheet 10 while the driving circuit 4 lights both of the fluorescent lamps 11A and 11B. While one of the fluorescent lamps 11A or 11B is turned on, one of the illumination lights LA2 or LB2 illuminates the LCD panel LP through the light diffusion sheet 10.

However, backlighting with almost the same directivity is achieved in either mode of operation. Thus, an easy-to-view screen is provided in almost the front direction. In addition, by changing the driving current of one or both of the fluorescent lamps 11A and 11B, the brightness of the screen can be freely adjusted in a very wide range. BACKGROUND OF THE INVENTION A drive circuit for adjusting the drive current of a light source using an inverter is known.

(2) 2nd Embodiment

12 and 13, an arrangement according to the second embodiment is drawn. As will be understood by comparing Figs. 12 and 13 with Figs. 1 and 2, the present embodiment is the same as the first embodiment except that the prism sheet 19 is employed instead of the prism sheet 9 as the light control member. It has the same layout. Although the prism sheet 19 may be the same as the prism sheet 9, it arrange | positions in a different orientation as mentioned later.

Therefore, this embodiment is described centering on the matter related to the prism sheet 19, and description of the matter common to 1st embodiment is simplified. In addition, the common code | symbol is attached | subjected to the member common to 1st Embodiment.

As in the case of the first embodiment (Figs. 1 and 2), the side light type surface light source device 1 is arranged for backlighting of the LCD panel LP, and constitutes the liquid crystal display device 2 (Fig. 13). have. The liquid crystal display device 2 is applied to a display in a car navigation system, for example.

The surface light source device 1 includes first and second light guide plates 7A and 7B, and correspondingly includes first and second primary light sources 3A and 3B and a drive circuit 4 for driving them. do. The first and second light guide plates 7A and 7B are stacked so that the second back surface is continuously disposed along the first exit surface. The light guide plates 7A and 7B have the same wedge-shaped cross section, and are arranged such that the exit surface 7AO is along the rear surface 7BR. The exit surface 7AO and the back surface 7BR provide inclined surfaces having substantially the same area, and the inclined surfaces face each other with a thin air layer therebetween. This arrangement provides a compact overall structure with the same thickness.

One minor surface of the first light guide plate 7A provides the first incident end surface 7AI. In addition, as shown by the circle B in FIG. 12, one minor surface of the second light guide plate 7B provides the second incident end surface 7BI. Incident cross sections 7AI and 7BI are located opposite to each other with respect to both light guide plates.

The structures, arrangements and functions of the primary light sources 3A and 3B and the drive circuit 4 are also common to the first embodiment. The drive circuit 4 incorporates an inverter and supplies electric power to one or both of the rod-shaped fluorescent lamps 11A and 11B. The power supply can be adjusted continuously or stepwise. Furthermore, not only simultaneous lighting and simultaneous lighting of both lamps but also one of the lights can be turned on and the other can be turned off.

The fluorescent lamps 11A and 11B are arranged along the incidence end surfaces 7AI and 7BI, respectively. One or both of the fluorescent lamps 11A and 11B supplies primary light to one or both of the light guide plates 7A and 7B according to the operation mode of the drive circuit 4.

As shown by the circle A in FIG. 12, many projection lines are formed on the back surface of the light guide plate 7A. Each projection includes a pair of inclined surfaces that are continuously disposed substantially perpendicular to the incidence end surface 7AI. The function of these protrusions is the same as that of the first embodiment. That is, the directivity (priority exit direction) of the light output at the exit surface 7AO (or at exit surface 7BO) acts closer to the front direction with respect to the plane parallel to the incident end surface 7AI.

In addition, the emission efficiency at the emission surface 7AO is improved, and light transmission to the light guide plate 7B is smoothly performed. The reflective sheet 8 disposed along the back surface 7AR reflects the light leaked from the back surface 7AR and returns to the light guide plate 7A, thereby preventing the loss of light energy. It is preferable that the light scattering pattern which promotes the emission from the light guide plate 7A or 7B is formed in one or both of the emission surfaces 7AO and 7BO. The detail of such a light-scattering pattern is as having described in description of 1st Embodiment.

The behavior of light when the fluorescent lamp 11A is ON alone, when the fluorescent lamp 11B is ON and simultaneous lighting of the fluorescent lamps 11A, 11B is the first embodiment as far as the incident light enters the prism sheet 19. Is the same as

When the fluorescent lamp 11A is on alone, the illumination light LA is introduced into the light guide plate 7A, transferred to the light guide plate 7B via various light paths, and exits from the exit surface 7AO. As described above, the directivity (priority emission direction) of the illumination light LA1 at the emission surface 7AO is close to the front direction with respect to the in-plane parallel to the incident end surface 7AI. Further, in the plane perpendicular to the incidence end surface 7AI, the inclination is greatly inclined forward (incidence end surface 7BI side).

On the other hand, when the fluorescent lamp 11B is turned on, the illumination light LB is introduced into the light guide plate 7B and exits from the exit surface 7BO via various light paths. The illumination light LB1 supplied from this illumination light and exiting from the exit surface 7BO is inclined greatly toward the front (incident cross section 7AI side) with respect to the plane perpendicular to the incident end surface 7BI.

In other words, the representative light sources LA1 and LB1 are in the plane perpendicular to the incidence planes 7AI and 7BI at the point of exit from the exit plane 7BO and with respect to the normal line (front direction) set up at the exit plane 7BO. It is greatly inclined to the opposite side. As described above, the inclination angle with respect to the exit surface 7BO of LA1 and LB1 in this example is about 23 degrees.

According to the characteristic of this embodiment, after passing through the prism sheet 19, the light beam LA1, LB1 becomes the light beam LA2, LB2 which advances in a different direction, respectively. The surface light source device 1 outputs the light beam LA2 when only the fluorescent lamp 11A is turned on, and outputs the light beam LB2 when only the fluorescent lamp 11B is turned on. When the fluorescent lamps 11A and 11B are simultaneously lit, the light beams LA2 and LB2 are output.

The directivity of the emitted light represented by LA1, LB1 is as described with reference to Figs. That is, in the measurement results of FIGS. 3 and 4, the illumination light represented by LA1 has a directivity inclined to the right in FIG. 14, and the illumination light represented by LB1 has a directivity inclined to the left in FIG. 14.

As depicted in Fig. 5, the two ridge curves are shown at angular positions that are nearly symmetric with respect to the front direction (Xθ = 0). One ridge corresponds to LA1, and the other ridge corresponds to LB1.

In this embodiment, the prism sheet 19 which bends the representative light beams LA1 and LB1 in the direction shifted from the front direction (Xθ = 0), respectively, and outputs the representative light beams LA2 and LB2 shown in FIG. 14 is employed. . In this example, the traveling directions of the representative rays LA2 and LB2 are almost symmetrical with respect to the front direction.

The prism sheet 19 is the same as the prism sheet 9 and is made of a light-transmitting sheet material such as polycarbonate, for example. The prism sheet 19 is disposed along the second emission surface 7BO in an orientation in which the prism surface faces the outer side (the light diffusing plate 10). A large number of protrusions are formed on the prism face.

As shown by circle C in FIG. 12, each of the protrusions includes pairs of inclined surfaces 19A and 19B that are continuously arranged substantially parallel to the incident end surface 7BI. The inclined surface pairs 19A and 19B are directly connected to each other, and a triangular cross section is given to each of the projection lines.

In the present embodiment, the right angle α is set to α = 66 degrees. The inclination angles (angle formed with respect to the general surface of the prism sheet 19) of the inclined surfaces 19A and 19B are equal to each other (inclined angle = 57 degrees). That is, the prism sheet 19 has the same prism angle as the prism sheet 9. Note, however, that this is not a general requirement and that prism sheets 9 and other prism angles are also allowed.

As shown in FIG. 14, the illumination light LA1 is introduced into the prism sheet 19 on the flat inner surface. The advancing direction of LA1 rises slightly by refraction. Next, it is output as illumination light LA2 from the inclined surface 19A. The direction of travel of LA2 also rises slightly further by the deflection of the burn.

On the other hand, the illumination light LB1 is introduced into the prism sheet 19 on the flat inner surface. The advancing direction of LB1 rises slightly by refraction. Next, it is output as illumination light LB2 on the inclined surface 19B. The advancing direction of LB2 also rises slightly by the deflection of the burn. Thus, it is correct | amended so that the advancing direction of LA2, LB2 may become closer to a front direction from both sides, compared with the advancing direction of LA1, LB1.

The operation of the prism sheet 19 in this example is easily understood in the graphs of FIGS. 15 to 17. FIG. 15 is a graph showing the directing characteristic of illumination light under conditions of illuminating the fluorescent lamp 11A (first primary light source) alone in the second embodiment. That is, the prism sheet 19 is added to the arrangement | positioning which obtained the result of FIG. 3, and the directivity characteristic of the output light of the prism sheet 19 is measured.

Similarly, FIG. 16 is a graph showing the directing characteristic of illumination light under the condition that the fluorescent lamp 11B (second primary light source) alone lights up in the second embodiment. That is, the prism sheet 19 is added to the arrangement | positioning which obtained the result of FIG. 4, and the directing characteristic of the output light of the prism sheet 19 is measured.

FIG. 17 is a graph showing directing characteristics of illumination light under conditions of simultaneously lighting the fluorescent lamps 11A and 11B (first and second primary light sources) in the second embodiment. That is, the prism sheet 19 is added to the arrangement | positioning which obtained the result of FIG. 5, and the directivity characteristic of the output light of the prism sheet 19 is measured.

It is understood that the output illumination light represented by LA2 in FIGS. 15 and 16 has a directivity inclined to the right in FIG. 13, and the output illumination light represented by LB2 has a directivity inclined to the left in FIG. 13. This is also understood in the two ridge curves shown in the graph of FIG. Naturally, the graph of FIG. 17 corresponds to the addition of the graph of FIG. 15 and the graph of FIG.

It should be noted here that the two ridge curves shown in FIG. 17 are closer to the front direction (Xθ = 0) than the two ridge curves shown in FIG. One ridge line in FIG. 17 corresponds to LA2, and the other ridge line corresponds to LB2.

The illumination lights LA2 and LB2 thus produced are subjected to weak diffusion in the light diffusion sheet 10 and then supplied to the liquid crystal display panel LP and contribute to display. The important point here is that since LA2 and LB2 have different directivities, one or two directions of bright display are observed depending on the lighting mode.

Since the illumination light LB2 is not output when the fluorescent lamp 11A is lit alone, the direction of the observer 5A becomes the observation direction suitable for observation. On the other hand, the illumination light LA2 is not output when the fluorescent lamp 11B is on alone, so that the direction of the observer 5B becomes an observation direction suitable for observation. In the simultaneous lighting of the fluorescent lamps 11A and 11B, of course, the direction of the observer 5A and the direction of the observer 5B become suitable directions for observation.

In the case where the liquid crystal display device 2 is applied to a car navigation system, it is preferable to assume the observers 5A and 5B as the assistants of the driver and the side seat, respectively, to design the output directions of the illumination lights LA2 and LB2.

In this case, when observing the LCD screen by the driver alone, it would be reasonable to light up the fluorescent lamps 11A or 11B alone. It is also sufficient if one of the two priorities is valid. When the LCD screen is observed by the assistant alone, it would be reasonable to light up the fluorescent lamps 11B or 11A alone. In addition, when both the driver and the assistant observe the LCD screen, the lighting of both lamps is reasonable.

(3) change

The above embodiment does not imply a limitation of the scope of the present invention. For example, many changes are allowed:

(a) In the said embodiment, a processus | protrusion line is formed in the back surface of a lower light guide plate, and the back surface of an upper light guide plate is a mirror surface. However, this does not limit the present invention. Projections may be formed on both rear surfaces. In addition, both rear surfaces may be mirror surface.

In addition, even if the projection line is formed on the exit surface of the lower light guide plate, the projection row may be formed on the exit surface of the upper light guide plate.

(b) The light-diffusion pattern formed on the exit surface of one or both light guide plates may be formed by other techniques, such as partial printing of white ink, for example. In addition, a design that does not form a light diffusion pattern in any light guide plate is allowed.

The light diffusion pattern may be formed on the rear surface of one or both light guide plates. A light diffusion pattern may be formed on both the emission surface and the rear surface.

(c) A light scattering light guide different from that described in the embodiment may be employed as the material of the light guide plate. Moreover, the transparent resin which does not have scattering power inside may be employ | adopted.

(d) In the above embodiment, one fluorescent lamp is provided corresponding to each light guide plate. However, an arrangement in which each light guide plate is supplied with primary light from a plurality of light source elements may be employed.

10 shows an example thereof. In this example, two rod-shaped fluorescent lamps are correspondingly arranged on each of two wedge-shaped light guide plates. A reflecting plate is provided behind each fluorescent lamp pair, and is arranged along the cross section of the thick side of each light guide plate as a primary light source. Since the combination of the lighting states of the respective fluorescent lamps is diversified, the brightness can be adjusted in a very wide range.

The arrangement as in this example is applicable to any type of device of the first embodiment type (monodirectional) and the second embodiment (bidirectional) depending on the characteristics of the prism sheet.

(e) Three or more light guide plates may be laminated. 11 and 18 show an example.

According to the example shown in FIG. 11, two units of the first embodiment type (single orientation) type are combined in an orientation relationship in which they are 90 degrees to each other. In this arrangement, since the combination of the lighting states of the respective fluorescent lamps is diversified, the brightness can be adjusted in a very wide range.

In addition, according to the example shown in FIG. 18, the unit which removed the prism sheet in the arrangement | positioning of 1st Embodiment or 2nd Embodiment is combined together by the orientation relationship which makes 90 degree mutually.

In this arrangement, since the combination of the lighting states of the respective fluorescent lamps is diversified, the range of switching of directivity is very wide. For example, directivity in four directions is obtained by selective single lighting of four fluorescent lamps.

(f) In the said embodiment, the prism sheet of 66 degree prism angle is employ | adopted. However, this does not limit the present invention.

As described, the value of the right angle is designed by design depending on the desired directivity. Generally, the prism sheet right angle can be appropriately selected within a range of 40 degrees or more, and therefore various directivities can be realized.

In addition, an arrangement in which the prism sheet is omitted is also allowed. In this case, generally two or more directions will be provided depending on the number of use of the light guide plate.

(g) The prism face of the prism sheet is inward in the first embodiment and outward in the second embodiment. In general, the direction of the prism face may be inward or outward as long as the desired directivity is given to the output illumination light.

Two or more prism sheets may be employed for the orientation correction. For example, two prism sheets may be arrange | positioned so that the continuous arrangement direction of an inclined surface may orthogonally cross. In this case, directivity correction is possible in the plane in two directions (parallel and orthogonal to the incidence cross section of the light guide plate). In addition, what is called a double-sided prism sheet may be employ | adopted.

The projection lines of the prism sheet need not be formed by direct connection of the inclined surfaces. For example, you may form a protrusion by connecting a pair of inclined surfaces to a curved surface. The inclined surface itself may be a curved surface.

(h) In the said embodiment, the light-diffusion sheet is arrange | positioned outside the prism sheet. However, this does not limit the present invention. For example, the light diffusion sheet may be removed. In addition, other elements, for example, a polarization separation sheet, may be disposed.

(i) In the said embodiment, the light guide plate of cross-sectional wedge shape is employ | adopted. Other light guide plates can be employed as long as preferential emission in an oblique direction from the emission surface occurs when primary light is supplied from the side cross section.

For example, instead of the wedge-shaped light guide plates 7A and 7B in the first embodiment or the second embodiment, two light guide plates having the same thickness as the whole may be laminated.

(j) In the above embodiment, the present invention is applied to a liquid crystal display device in a car navigation system. However, the present invention may be applied to a liquid crystal display device for another device such as, for example, a PC. Further, the present invention can be widely applied to various lighting devices and display devices other than the liquid crystal display device.

According to the above description, the present invention can adjust the intensity of the illumination light output over a wide range, and by applying it to a liquid crystal display device, it is possible to easily obtain good display without being influenced by the environment, and also has illumination in two directions. The output is provided and applied to the liquid crystal display device so that a display suitable for observation in two different directions, in particular in one of those two directions, is obtained.

Claims (24)

A first light guide plate, a first primary light source arranged in parallel with the first light guide plate, a second light guide plate, a second primary light source arranged in parallel with the second light guide plate, the first primary light source and the second primary light source In the side light type surface light source device having a driving circuit for driving, Two minor surfaces of the first LGP provide a first exit surface and a first back surface, while one minor surface of the first LGP provides a first incident cross section, Two minor surfaces of the second light guide plate provide a second exit surface and a second back surface, and one minor surface of the second light guide plate provides a second incident cross section, The first light guide plate and the second light guide plate are laminated so that the second rear surface is continuous along the first emission surface, The first incident cross section and the second incident cross section are located opposite to each other with respect to the stack arrangement; And a light control member for controlling directivity of the illumination output light along the second emission surface. The side light type surface light source device according to claim 1, wherein the driving circuit can extinguish only one of the first and second primary light sources. The side light type according to claim 1, wherein the first light guide plate and the second light guide plate each have a wedge-shaped cross section, and the first incident cross section and the second incident cross section are located on a thick side of the wedge shape. Surface light source device. The light guide plate of claim 2, wherein the first light guide plate and the second light guide plate each have a wedge-shaped cross section. And said first incident cross section and said second incident cross section are located on the thick side of the wedge shape. 2. The sidelight type surface according to claim 1, wherein a plurality of protrusion lines are formed on the first back surface, and each of the protrusion lines includes a pair of inclined surfaces that are disposed substantially perpendicular to the first incident cross section. Light source device. 3. The sidelight type surface according to claim 2, wherein a plurality of protrusion lines are formed on the first rear surface, and each of the protrusion lines includes a pair of inclined surfaces that are continuously disposed substantially perpendicular to the first incident cross section. Light source device. 4. The sidelight type surface according to claim 3, wherein a plurality of protrusion lines are formed on the first back surface, and each of the protrusion lines includes a pair of inclined surfaces that are continuously disposed substantially perpendicular to the first incident cross section. Light source device. 5. The sidelight type surface according to claim 4, wherein a plurality of protrusion lines are formed on the first rear surface, and each of the protrusion lines includes a pair of inclined surfaces that are continuously disposed substantially perpendicular to the first incident cross section. Light source device. The light control member according to any one of claims 1 to 8, further comprising: a light control member for controlling directivity of the illumination output light along the second emission surface; The light control member corrects the directivity toward the front direction of the second emission surface for both the illumination output light output by the first primary light source and the illumination output light output by the second primary light source. Side light type surface light source device. 10. The side according to claim 9, wherein a plurality of projection rows are formed on an inner surface of the light control member, and each of the projection rows includes a pair of inclined surfaces that are continuously disposed substantially parallel to the second incident end surface. Light type surface light source device. The light control member according to any one of claims 1 to 8, further comprising: a light control member for controlling directivity of the illumination output light along the second emission surface; The light control member is adapted to correct directivity in two different directions with respect to the illumination output light output by the first primary light source and the illumination output light output by the second primary light source. Light source device. 12. The side according to claim 11, wherein a plurality of projection rows are formed on an outer surface of the light control member, and each of the projection rows includes a pair of inclined surfaces that are continuously disposed substantially parallel to the second incident end surface. Light type surface light source device. A liquid crystal display device comprising a liquid crystal display panel and a side light type surface light source device for backlighting the liquid crystal display panel. The side light type surface light source device includes a first light guide plate, a first primary light source arranged in parallel with the first light guide plate, a second light guide plate, a second primary light source arranged in parallel with the second light guide plate, and the first primary light source. A light source and a driving circuit for driving the second primary light source, Two minor surfaces of the first LGP provide a first exit surface and a first back surface, while one minor surface of the first LGP provides a first incident cross section, Two minor surfaces of the second light guide plate provide a second exit surface and a second back surface, and one minor surface of the second light guide plate provides a second incident cross section, The first light guide plate and the second light guide plate are laminated so that the second rear surface is continuous along the first emission surface, The first incidence cross section and the second incidence cross section are located on opposite sides with respect to the lamination arrangement, And a light control member for controlling the directivity of the illumination output light along the second emission surface. 14. The liquid crystal display device according to claim 13, wherein the driving circuit can extinguish only one of the first primary light source and the second primary light source. The method of claim 13, wherein the first light guide plate and the second light guide plate each has a wedge-shaped cross section, And the first incident cross section and the second incident cross section are located on the thick side of the wedge shape. The method of claim 14, wherein the first light guide plate and the second light guide plate each has a wedge-shaped cross section, And the first incidence end surface and the second incidence end surface are located on the thick side of the wedge shape. 15. The liquid crystal display device according to claim 13, wherein a plurality of projection lines are formed on the first back surface, and each of the projection lines includes a pair of inclined surfaces that are continuously disposed substantially perpendicular to the first incident cross section. 15. The liquid crystal display device according to claim 14, wherein a plurality of projection lines are formed on the first rear surface, and each of the projection lines includes a pair of inclined surfaces that are continuously disposed substantially perpendicular to the first incident cross section. 16. The liquid crystal display device according to claim 15, wherein a plurality of protrusion lines are formed on the first rear surface, and each of the protrusion lines includes a pair of inclined surfaces that are continuously disposed substantially perpendicular to the first incidence end surface. 17. The liquid crystal display device according to claim 16, wherein a plurality of projection lines are formed on the first back surface, and each of the projection lines includes a pair of inclined surfaces that are disposed substantially perpendicular to the first incident cross section. The light control member according to any one of claims 13 to 20, wherein the light control member is adapted to either the illumination output light output by the first primary light source or the illumination output light output by the second primary light source. 2 A liquid crystal display device characterized by correcting the directivity toward the front direction of the exit surface. 22. The liquid crystal of claim 21, wherein a plurality of projection rows are formed on an inner surface of the light control member, and each of the projection rows includes a pair of inclined surfaces that are continuously disposed substantially parallel to the second incident end surface. Display. 21. The light control member according to any one of claims 13 to 20, wherein the light control member has two different directions with respect to the illumination output light output by the first primary light source and the illumination output light output by the second primary light source. Liquid crystal display device characterized in that to modify the directivity toward the. 24. The liquid crystal of claim 23, wherein a plurality of projection rows are formed on an outer surface of the light control member, and each of the projection rows includes a pair of inclined surfaces disposed substantially parallel to the second incident end surface. Display.